Disturbed Turnstones

blog facingIn a 2020 paper, Mark Whittingham and colleagues show that, in one area of northeast England, the decline in Turnstone numbers is more obvious on mainland sites that are subject to human disturbance than on offshore refuges. Whilst national declines are probably linked to factors affecting productivity in breeding areas in Greenland and Canada, it is interesting that Turnstone seem to be withdrawing into areas where they are subject to less winter disturbance.

Turnstones – some background

The Turnstones that we see around the coastline of Britain and Ireland in the winter are almost exclusively birds that fly here from Greenland and eastern Canada, as you can read in this blog about wader migration (Which wader, when and why?). Britain’s wintering Turnstone numbers are falling, as are populations of several other species, such as Curlew, Oystercatcher, Knot and Redshank (see Do population estimates matter?). Turnstones are opportunist feeders; although traditionally thought of as rocky coast specialists, they can also be found on muddy estuaries and around beach-bars in the Caribbean (Why do Turnstones eat chips?).

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Measuring disturbance

Assessing the effects of disturbance during the winter is not easy. Feeding waders may be flushed by bait-diggers, kayakers, dog-walkers etc. but is this an issue if the food that they were attempting to eat becomes available later? To demonstrate that disturbance is a real problem, one would ideally demonstrate reductions in fitness measures such as survival, recruitment and/or productivity. This is discussed in a paper by Jenny Gill and colleagues, who studied the potential effects of disturbance on feeding Black-tailed Godwits (paper in Journal of Applied Ecology) and in another paper by Colin Beale and Pat Monaghan that shows that well-fed Turnstones were quicker to respond to disturbance than birds that had not received supplementary food supplies (Animal Behaviour).  Birds may be quicker to fly if they are well-fed or there is somewhere else where they can feed. The ones that have no choice and are still hungry may be the last to leave. The issue is discussed more widely in Why behavioural responses may not reflect the population consequences of human disturbance.

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It’s not just waders : Little Egret being chased  along the shores of the River Bann SPA and (below) the last few Brent Geese being removed from saltmarsh on the Exe Estuary (SPA)

Potentially, roosting waders could be more prone to disturbance than feeding birds, because of the wasted energy associated with flying around over the high-tide period or relocating to an alternative roost site (see A place to roost). An interesting modelling paper by Mark Rehfisch and colleagues showed that 90% of Dunlin, Grey Plover and Redshank on the Wash could be serviced by roost sites that were 2 km, 2.5 km and 3.5 km apart, respectively (Applied Ecology). These numbers may or may not be comparable for Turnstone but do suggest that small- to medium-sized waders feed within relatively short distances of their preferred roosting areas.

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Turnstone in this study

Turnstone is a species of qualifying interest for the Northumbria Coast Special Protection Area (SPA) and for several Sites of Special Scientific Interest (SSSI) in the region. On this 140 km stretch of coast, the population of Turnstone declined by 27% between 2004/5 and 2009/10, during a period when the wintering number within England declined by 9%. There was concern that human disturbance may be one of the drivers of the population decline of wintering Turmstone within the SPA. Potentially such conditions could become more challenging towards the end of the winter, when food supplies may be less and birds are preparing for migration, or during periods of very cold weather. Given an increase in the local human (and canine) population and a marked rise in tourism within the region, it was suggested that the potential for disturbance may have increased.

 

study area

The aim of the study was to compare wintering Turnstone densities and changes in counts across time from sites with differing levels of human disturbance. This was possible because long-term Wetland Bird Survey counts of waders had been made in the period between 1998/99 and 2015/16. Counts were available for two offshore refuges and 17 mainland sites that were subject to higher levels of human disturbance. No direct measure of human disturbance was available so questionnaires were used to determine the behaviour of beach users, in terms of distance travelled to visit the coast. The paper contains full detail of this methodology.

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Results

After controlling for the extent of preferred habitat (rocky shore) at each site the authors found that:

  1. The closer each of the 19 sites was to the nearest offshore refuge the higher the density of Turnstones, where density is calculated as birds per hectare of suitable feeding habitat.
  2. Turnstone counts at the four sites closest to, or containing, offshore refuges showed no significant declines. Despite the national decline in the number of wintering Turnstones, the counts on the Farne Islands and on St. Mary’s Island (both offshore islands) rose during the study period, although the rate of increase was not statistically significant from zero. There were declines at 15 of the 17 non-refuge sites. These results are consistent with the idea that, as populations decline generally, the sites of the highest quality (in this case those subject to less human disturbance) will show no, or slower, declines.
  3. 65% of the walkers interviewed on beaches were exercising their dogs, 83% having travelled 6 km or less to get to the beach. No relationship was found between Turnstone counts and human population densities. There is more information in the paper about the amount of time that people spend on different types of beaches.
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Graph showing Turnstone densities at different distances from refuges on the coast of northeast England. Figure from paper in Bird Study.

 

Implications

The authors of the Bird Study paper have not sought to explain declines in Turnstone numbers, but they have provided some useful references in the Discussion that highlight how improved water treatment and warmer winters might have affected regional distributions. They also remind us that Turnstone numbers are declining – as is the case for several High Arctic species. Having established that there are declines, they use the pattern of change to ask questions about whether disturbance is an issue for this species.

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Seahouses, looking out towards The Farnes – not far, as the Turnstone flies

The results of the research suggest that Turnstones make greater use of relatively undisturbed areas (offshore refuges) than those subject to greater disturbance by humans and their four-legged friends. Previous work has shown that excessive disturbance prevents the use of roosts and that disturbance can have serious energetic consequences (see A place to roost). Although the paper does not distinguish between birds that are foraging or roosting, this study suggests greater provision of undisturbed sites (refuges) within, or close to, protected areas is important for Turnstones, especially if there is also a drive to build more houses and attract more tourists.

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Beaches at Seaburn (County Durham) and Ross Back Sands (Northumberland). Proximity to human settlement makes a big difference! There are 15 dogs in the left-hand picture.

When looking at the planning process for developments close to SPAs, Mark Whittingham and his colleagues suggest that three issues need to be considered in some detail:

  1. While it is valuable to consider the SPA as a whole, it is also important for decision-makers to consider the vulnerabilities of constituent parts of the site.  Thus, for planning decisions based upon environmental impact assessments, there is clearly a need to consider pressures on particularly vulnerable areas, e.g. those used for roosting.
  2. blog tagged

    One of the tagged individuals that was tracked as part of a complementary study

    Studying the behaviour of marked individuals might help to pinpoint areas that are of critical importance. A separate, small-sample study of radio-tagged Turnstones in the area showed that these birds avoided mainland feeding and roosting areas at night, with at least some of the tagged Turnstones being found on offshore sites.

  3. Species need to be considered separately when assessing disturbance issues because habitat use and resource distribution varies widely. The focus for Turnstones is on rocky coasts and this determines their choice of roosting sites. The requirements of red-listed Ringed Plover (for instance) may be very different, especially as they spend a lot of time feeding on the sort of open beaches that look great for exercising dogs.

Paper

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Dogs are an important part of the disturbance issue.

The paper at the heart of this blog is:

Offshore refuges support higher densities and show slower population declines of wintering turnstones by Mark J. Whittingham, Ailsa J.  McKenzie, Richard M. Francksen, David Feige, Tom Cadwallender, Matthew Grainger, Nadheer Fazaa, Caroline Rhymer, Catherine Wilkinson, Pauline Lloyd, Ben Smurthwaite, Steve M. Percival, Tammy Morris-Hale, Clare Rawcliffe, Claire Dewson, Sarah Woods, Gavin B. Stewart & Elizabeth Oughton. Bird Study DOI  10.1080/00063657.2020.1713725


GFA in IcelandGraham (@grahamfappleton) has studied waders for over 40 years and is currently involved in wader research in the UK and in Iceland.  He was Director of Communications at The British Trust for Ornithology until 2013 and is now a freelance writer and broadcaster.

 

 

WaderTales blogs in 2019

Nineteen new WaderTales blogs were published during 2019. Click on a link in bold to read an individual blog.

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Ringed Plovers often have time to nest again if the first clutch is lost

Over 25,000 people, representing 130 countries, visited the WaderTales website during 2019.

  • The most widely-read blog was Ireland’s Curlew Crisis, reflecting the international concern for the species and the culew family as a whole.
  • It is great that the next most popular blog is Managing water for waders, as this is such a positive story about how farmers, conservation organisations and statutory agencies can work together to deliver better habitat for breeding waders and an improved water supply for farmers.
  • In third place is Sixty years of Wash waders which describes six decades of scientific outputs of the Wash Wader Ringing Group. The WWRG’s founder, Clive Minton, died in tragic circumstances just a couple of months later and there are some lovely tributes here, on the International Wader Study Group website.

Migration

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The distinctive white under-wing of a Steppe Whimbrel

The migration blogs cover a wide range of species:

  • Generational Change uses colour-ring sightings to explore how Black-tailed Godwit populations have changed in distribution and migratory timing.
  • Whimbrel: time to leave summarises a paper about the consistencies and variability of annual migration patterns of individual Whimbrel.
  • Red Knot pay the price for being fussy eaters discusses the reliance of Delaware Bay birds on the unpredictable annual supply of horseshoe crab eggs. Why are Ruddy Turnstones better able to cope in a changing world?
  • Not-so-Common Sandpipers mixes information about migration with a review of Common & Spotted Sandpipers by Phil Holland.
  • Travel advice for Sanderling summarises research to understand the pros & cons of spending the non-breeding season in widely different locations. Birds in equatorial Africa do far less well than those in England and Namibia.
  • In search of Steppe Whimbrel summarises a paper about two very special individual Whimbrel. Will this knowledge help to rescue a subspecies?

Breeding waders

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Redshanks need long grass in which to hide their nests

There is bad news for Curlew and Redshank, some interesting information about the effects of ticks on chicks and an important stock-take of Fennoscandia’s breeding waders.

  • Redshank – the ‘warden of the marsh’ focuses on Redshank that breed on saltmarshes and the agricultural subsidies that help to fund their conservation.
  • From local warming to range expansion explores the role of climate warming in fuelling the century-long range expansion of Iceland’s Black-tailed Godwit population.
  • Ireland’s Curlew Crisis focuses on the nationwide breeding survey between 2015 and 2017, which revealed a 96% decline in the number of pairs in the previous 30 years.
  • Chicks and Ticks reviews a study of the effects of ticks on the survival probability of Golden Plover chicks.
  • Fennoscandian wader factory summarises analyses of breeding wader numbers in Finland, Sweden and Norway over the period 2006 to 2018.
  • Managing water for waders celebrates work to reduce flooding, store fresh water for farmers and create habitat for breeding waders.
  • Time to nest again? asks how much of the advantage of being an early migrant could be associated with having an option to nest again, if the first attempt fails.

Winter waders 

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Winter numbers of Oystercatcher and Knot have declined in Britain and Ireland

The Green Sandpiper blog reveals unpublished information about territoriality. The other two blogs in this section summarise population estimates of waders in Great Britain and Ireland, based on new papers in British Birds and Irish Birds.

  • Winter territories of Green Sandpipers includes unpublished information from southern England, where survival is affected by the severity of winters.
  • Do population estimates matter? is inspired by the waders section of Population estimates of wintering waterbirds in Great Britain, based on data from the Wetland Bird Survey and the Non-estuarine Waterbirds Survey.
  • Ireland’s wintering waders complements the above blog, providing information from I-WeBS and WeBS for the island of Ireland and set in a European context.

The others!

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Adding colour rings and individual flags to Grey Plover

One of the aims of these blogs is to engage people in projects that are in need of volunteers or other forms of public engagement – hence the Northern Ireland blog. The other two articles celebrate sixty years of The Wash Wader Ringing Group and share concerns about a new airport for Lisbon, to be built right next to the Tagus/Tejo Estuary.

  • The Waders of Northern Ireland was written as a promotional tool for a 2019 breeding survey but covers wintering and passage species too.
  • Sixty years of Wash waders celebrates the longest-running wader-ringing project in the UK  (and the world?), by summarising six decades of migration research.
  • Tagus estuary: for birds or planes? What could go wrong if an international airport is built right next to an estuary that is important to Black-tailed Godwits?
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Vast flocks of Black-tailed Godwit gather in the Tagus Estuary in February

WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research. Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.The intention is to add one or two new blogs each month. You can sign up to receive an e-mail notification when a new one is published. Full list of blogs here.


GFA in IcelandGraham (@grahamfappleton) has studied waders for over 40 years and is currently involved in wader research in the UK and in Iceland.  He was Director of Communications at The British Trust for Ornithology until 2013 and is now a freelance writer and broadcaster.

Tagus estuary: for birds or planes?

blog samoucoA planned new airport that will serve Lisbon threatens the future of internationally important flocks of waders and other waterbirds. These same birds pose safety concerns for the passenger aircraft that will fly through the airspace that is currently reserved for them.

The development site of the proposed Montijo airport abuts the part of the Tagus/Tejo estuary that is designated as a Special Protection Area (SPA) and an Important Bird Area (IBA). This designation is based upon counts of 49,000 Black-tailed Godwits, 12,000 Dunlin, 6000 Avocet, 4500 Wigeon, 3300 Greylag Geese, 2000 Grey Plover and 1600 Greater Flamingos. That’s 23 tonnes of birds, representing just a few key species, before you add in gulls, Spoonbills and up to 6,000 Glossy Ibises. This blog focuses upon the importance of the Tagus/Tejo Estuary for just one of the species, the Black-tailed Godwit.

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The planning process

At first sight, turning the air force base in Montijo into a commercial airport looks like an obvious option, given that planes already take off and land there. However, the runway will need to be longer, there will have to be a vast new infrastructure and planes will be landing every few minutes, rather than during scheduled periods of military training. There will be some habitat removal, and it will be hard to avoid run-off of fuel and chemicals into the estuary, but the big problem will be disturbance of the flocks of birds within this IBA, as planes land and take-off and when airport employees frighten away flocks that are too close to the main flight-paths. Each time a flock of birds takes to the air, a large amount of fuel is burnt – as fat laid down for migration is wasted.

blog flamingoPlanes and birds do not mix, as we saw on 15 January 2009, when US Airways Airbus Flight 1549 landed on the Hudson River after an encounter with Canada Geese. How many Greater Flamingos will it take to stop a jet engine? Each one weighs about three kilogrammes and there are 1600 on the SPA, many within a few hundred metres of the airport site.

Around the world, there have been many bird/plane incidents, some causing significant loss of (human) life, which explains why there’s not a ‘Boris Island Airport’ in the Thames Estuary. History suggests that bird-strike risks are underplayed at the planning stage but have to be coped with later. Once the airport is operational, it is likely that nests will be removed and attempts will be made to disperse flocks through disturbance and shooting.

Icelandic Black-tailed Godwits

The Tagus is particularly important for Black-tailed Godwits. Although the published count, associated with the designation of the estuary, is 49,000, it is agreed that the maximum late-winter number for the estuary and surrounding rice fields is now 70,000 or more, which includes birds of both the islandica and limosa races.

mapThere are Black-tailed Godwits on the Tagus during every month of the year. Numbers are lowest in the summer, chiefly comprising young islandica birds that do not travel back to Iceland in their first spring. Adults arrive back from Iceland between July and November, the later birds having stopped off to moult in sites such as the Wash (Eastern England) and coastal France. Numbers drop again as early as January, when adults move to the Netherlands and England, to fatten up for the trip back across the Atlantic to Iceland. There is a blog about this ‘overtake manoeuvre’ and the advantages it confers.

Given that islandica Black-tailed Godwits can spend the winter anywhere between Scotland and the south of Spain, it could be argued that disturbance on the Tagus, to try to disperse flocks, would be no big problem, as there are other places for individuals to spend the winter. Two things are wrong with this theory. Firstly, as was described in Generational Change, individual Black-tailed Godwits are creatures of habit, typically using a suite of about four non-breeding sites during their entire lives. If a Black-tailed Godwit is on a patch of mud in December one year then it will be back there the next year, and possibly for the next twenty.

blog RedshankThere is no reason to believe that Black-tailed Godwits are unique in being site-faithful. In the WaderTales blog called A place to roost there is a description of the consequences of site removal for Redshank in Cardiff Bay. Birds displaced by the flooding of the bay had much lower survival rates in the next year and in subsequent years than other Redshank with which they shared their new winter homes. This illustrates the second point; even though these Redshank were only forced to move a few kilometres, they were still severely disadvantaged.

Limosa Black-tailed Godwits

The Tagus really comes into its own during the late winter, as limosa Black-tailed Godwits pour into the area, en route to their breeding grounds in continental Europe. An increasing number of the limosa subspecies now spend the winter on the estuary and in surrounding fields but numbers grow rapidly in January, as others join them from sites as far south as Guinea, in West Africa. On the Tagus, they moult into summer plumage and build up fat reserves that will fuel flights to The Netherlands and surrounding countries, and prepare them for the breeding season that lies ahead. A favourite rice field may hold up to 70,000 Black-tailed Godwits in late February, which includes half of what’s now left of the Dutch breeding population. This is also where many of the birds that are heading back to the Nene and Ouse Washes of Eastern England fuel up for the final leg of their journeys home. Several of the Project Godwit head-started birds (youngsters raised from eggs and released when just about to fledge) have been seen on the Tagus in February.

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To watch vast feeding flocks of Black-tailed Godwits, or their swirling aerial displays, when disturbed by a hunting Peregrine, is an amazing experience – a highlight for locals and for visiting birdwatchers, who holiday here in late winter and early spring. It’s especially impressive to watch the godwits at dusk, when clouds of Glossy Ibis create a backdrop to the action, as they move off the fields and cross the IBA to roosting islands on the far side of the estuary.

blog take offAs indicated earlier, The Tagus Estuary is designated as an EU Special Protection Area because of its crucial role in the lives of a suite of species, just one of which is the Black-tailed Godwit. Over the last few years, the average peak godwit numbers on the Tagus and Sado Estuaries in Portugal have risen from 44,000 to 51,000, at the same time as the breeding population of the subspecies has dropped rapidly (see this WaderTales blog about 75% drop in Dutch numbers). The Portuguese increase has coincided with a rapid decline in spring totals in Extremadura (Spain).

Without colour-rings, it might be assumed that individual Black-tailed Godwits have changed their migration routes, suggesting a flexible response to changing conditions. This is not the case. In their paper, Generational shift in spring staging site use by a long-distance migratory bird, Mo Verhoeven and colleagues show that nearly all of the older birds stick to the routes that they know, with young birds establishing routes that are more likely to include the Tagus and Sado Estuaries. Western Portugal has become vitally important to limosa Black-tailed Godwits, a subspecies that is in huge trouble and upon which millions of conservation Euros are being spent in The Netherlands and elsewhere.

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What next?

The Portuguese Environmental Agency (Governmental institution) has given the go-ahead for the development of the airport at Montijo, despite robust arguments from researchers and conservationists about the inevitable effects on the IBA, and errors and limitations they have identified within the Environmental Assessment Study. There are also concerns about flooding risk, air pollution and other issues that seem not to have been fully assessed.

AEWASPEA, the Portuguese BirdLife partner, together with wader researchers who have studied waterbirds in the Tagus for decades, have submitted a request to the UNEP African-Eurasian Migratory Waterbirds Agreement (AEWA) to open an Implementation Review Process, to help Portugal to ensure that it complies with its obligations as a signatory to the treaty. The approach to AEWA is particularly appropriate for Black-tailed Godwits, as AEWA has already published a Single Species Action Plan to try to support efforts to restore populations of the rapidly declining limosa subspecies.

Black-tailed Godwits may be the most numerous of the key waterbird species for which the Tagus/Tejo Estuary is designated but let’s not forget the next most numerous six: 12,000 Dunlin, 6000 Avocet, 4500 Wigeon, 3300 Greylag Geese, 2000 Grey Plover and 1600 Greater Flamingos.

flamingo and ibis

Key conservation point

The most important conservation fact to bear in mind is that, as has been shown for Black-tailed Godwits, individual birds tend to be remarkably inflexible. Circumstances determine the migration pattern in the first year of life and, if a bird survives, it will continue to do the same things in subsequent years. Building an airport and then trying to reduce plane/bird interactions will quite probably affect the quality of the IBA for waders and other species. Individuals are unlikely to move elsewhere; they are more likely just to try to cope with altered circumstances. Habitat loss and disturbance on this scale are very likely to result in high levels of mortality and declines in the numbers of birds using this critically important site on the East Atlantic Flyway.

What now?

The Black-tailed Godwit is the Dutch national bird. The BirdLife partner in the Netherlands, Vogelbescherming, launched a petition to register Europe-wide concern about the Portuguese decision to build the new airport. Together with many other international conservation organisations, they are supporting legal challenges to the project that are being led by SPEA, the Portugues BirdLife partner. More here.

Not only will the new airport be a disaster for the East Atlantic Flyway, it also sets a precedent for developments affecting other Europe wetlands.

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GFA in Iceland

Graham (@grahamfappleton) has studied waders for over 40 years and is currently involved in wader research in the UK and in Iceland.  He was Director of Communications at The British Trust for Ornithology until 2013 and is now a freelance writer and broadcaster.

Fennoscandian wader factory

 

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Nesting Temminck’s Stint – the smallest of the 22 wader species for which trends are reported

At the end of the summer, vast numbers of waders leave Norway, Sweden and Finland, heading southwest, south and south-east for the winter. In a 2019 paper by Lindström et al, we learn what is happening to these populations of Fennoscandian breeding species, as diverse as Temminck’s Stint and Curlew. The news for the period 2006 through to 2018 is basically pretty good – most populations have been stable and there are even some that have increased – but there are worrying signs for Broad-billed Sandpiper, Red-necked Phalarope and Whimbrel.

Breeding waders of Fennoscandia

blog mapAs a volunteer taking part in the Breeding Bird Survey (BTO/JNCC/RSPB) in the UK, I feel that I do my bit to monitor what is happening to local bird population – providing counts that build into national trends. The work involved in delivering indices for breeding waders across the area of Fennoscandia shown in the map is in a different league. Here, counters visit habitats as diverse as forests, wetlands, mires and tundra, within the boreal and arctic areas of Norway, Sweden and Finland. Some survey sites are so remote that access requires the use of helicopters.

Fennoscandia provides important breeding areas for a large set of wader species, and models suggest that these habitats may be particularly vulnerable to climate change, especially increasing summer temperatures. The 2006-18 analysis in Wader Study, the journal of the International Wader Study Group, presents population trends for 22 wader species. The trends are based on 1,505 unique routes (6–8 km long), distributed over an area that’s about four times that of the United Kingdom. 

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The surveys took place across the whole of Norway and Finland, and in the northern two thirds of Sweden, between 58°N and 71°N, which largely coincides with the boreal, montane and arctic regions of Fennoscandia. The systematic distribution of these routes ensures that the main habitats in these countries are sampled in proportion to the area they cover. The paper describes the methodologies used in the three countries and the way that data were combined, especially factors used to translate sightings of individuals into ‘pair-equivalents’.

Overview of results

blog mountainLooking at the results from across Norway, Sweden & Finland:

  • In terms of pure numbers, Golden Plover was the most commonly encountered wader species, followed by Wood Sandpiper, Snipe, Greenshank and Green Sandpiper.
  • The five most widespread species, seen on the highest number of routes, were Snipe, Green Sandpiper, Greenshank, Wood Sandpiper and Common Sandpiper.
  • Wader species richness and the total number of wader pairs were both higher with increasing latitude; the median number of wader pairs per 10 km increased from just below 3 at latitudes 58–60°N, to just above 26 at latitudes 69–71°N.
  • Using a multi-species indicator, the research team found no general change in wader numbers over the period 2006-18.
  • The trends were significantly negative for three species: Red-necked Phalarope (-7.9% per year), Broad-billed Sandpiper (-5.4% per year) and Whimbrel (-1.3% per year).
  • The trends were significantly positive for three species: Oystercatcher (+4.9% per year), Dunlin (+4.2% per year) and Wood Sandpiper (+0.8% per year).
  • There was no significant trend for another 16 species for which encounters were deemed to be frequent enough for analysis.
  • Population trends of long-distance migrants tended to be more negative than those of medium-distance migrants. This is discussed in detail in the paper.

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Focusing on some key species

The Lindström et al paper is a tremendously rich source of information and references. Here are some species-specific highlights.

Oystercatcher. In the context of a species that is declining across NW Europe, the fact that there is a significant increase in Oystercatchers across Fennoscandia may be surprising. However, the authors note that there was a jump in numbers between 2006 and 2007 with little change since then.

blog l graphLapwing. The trends within the three Fennoscandian countries are very different. In Norway, there has been a dramatic decline (-15.2% per year during 2006–2018) and the Lapwing is now nearly extinct in many areas. The trend in Sweden is also significantly negative (-5.8% per year). In Finland, however, where the species is more widespread and numerous, there has been a strong increase (+5.9% per year) during the same period. See figure alongside.

Golden Plover. No significant change overall. There are some country-specific differences in trends, with a moderate decline in Norway being countered by a moderate increase in Sweden. 

Snipe. The overall trend of this species for each country indicates an initial decline followed by an increase. A similar pattern has been noted in the UK’s Breeding Bird Survey over the same period. 

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Nesting Whimbrel

Woodcock. The trend for 2006–2018 is basically stable and similar in all three countries.

Curlew. There is no significant trend, overall, but populations in Norway and Sweden have declined at the same time that numbers in Finland have increased.

Whimbrel. Fennoscandian trend indicates a decline of 1.3 % per year. Whimbrel is doing poorly in Norway and Sweden but better in Finland. 

Wood Sandpiper. This widespread species has increased slowly (0.8% per year), a trend that is largely driven by Norwegian and Swedish populations.

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Wood Sandpiper was the second most commonly encountered wader

Redshank. The fact that no change was discernible, suggests that boreal and arctic populations are faring much better than the breeding populations further south in Europe. For example, see Redshank – warden of the marsh.

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Redshank – more obvious than most breeding waders encountered!

Spotted Redshank. The estimated annual decline for Spotted Redshank is 2.8% per year but the species is too thinly spread for this to provide significant evidence of a decline. This rate is very similar to the recent drop in the Wetland Bird Survey index in the UK. See Fewer Spotted Redshanks.

Broad-billed Sandpiper. This species has the second most negative trend among the 22 species analysed (-5.6% per year). The bulk of information comes from Finland where the trend is even more negative (-7.5% per year). Birds head southeast in the autumn to countries bordering the Indian Ocean – areas for which winter trend data are not available. The species is still considered to be of ‘least concern’ but perhaps this designation may need to be revisited?

Dunlin. Breeding birds in the survey area are largely of the alpina race. The overall trend is significantly positive (+4.1% per year), which is in sharp contrast to the strong declines of the schinzii subspecies that breeds around the Baltic Sea, western Finland and further south and west in Europe.

blog rnpRuff. There were major declines in the period immediately prior to this review (Lindström et al. 2015) but changes reported here are lower (-2.3% per year) and the decline is not statistically significant.

Red-necked Phalarope. The authors write, “This species has the most negative trend of all the 22 species [-7.9% per year], with most data coming from Sweden. We do not know the cause of this decline but, given that this species shares its south-eastern migration route with Broad-billed Sandpiper, whose population exhibits the second largest decline, the relevant problems might largely apply somewhere along the migration routes”.

Link to Britain & Ireland

As shown in Which wader when and why? there are strong migratory connections between Fennoscandia and the British Isles. Some waders, such as Green, Common and Wood Sandpipers, pass through on their way south in the autumn, whilst many more fly here for the winter, to take advantage of the warmer maritime climate.

Three wader species with particularly strong links between Fennoscandia and Britain & Ireland are still shot and eaten in these islands. Each autumn, large numbers of Woodcock, Golden Plover and Snipe cross the North Sea. It is difficult to ascertain figures for the number that are shot but there is agreement that the vast majority are winter visitors, as opposed to native birds. The results presented in the paper suggest that there have been no discernible changes in the Fennoscandian populations of these three game species in the period 2006-18. Two earlier WaderTales blogs focus on Woodcock and Snipe in Britain & Ireland:

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There has been no significant change in Golden Plover numbers across Fennoscandia

Two WaderTales blogs about wintering waders in Great Britain and the island of Ireland were published in 2019, based on reviews in British Birds and Irish Birds. These were Do population estimates matter? and Ireland’s wintering waders. The six big losers, in terms of wintering numbers in these islands, were Knot, Oystercatcher, Redshank, Curlew, Grey Plover and Dunlin. Knot arrive from Greenland and Canada, with Grey Plover flying from Russia, but it is interesting to think about this Fennoscandian breeding analysis in the context of winter losses of the other four species.

  • Wintering numbers of Oystercatchers have dropped recently in Britain and in Ireland. The population is made up of migrants from Iceland (more about this here), very large numbers from Norway, birds that stay within the British Isles and smaller numbers from other European and Scandinavian countries. Given there is no discernible decline in Fennoscandia, it seems likely that much of the decline can be attributed to a major fall in Scottish breeding numbers (more about this here).
  • Most Redshank wintering in Britain & Ireland are of local or Icelandic origin. Fennoscandian numbers seem to be stable; if there were any changes, these would probably not be apparent in wintering numbers within the British Isles.
  • The Eurasian Curlew has been classified as ‘near-threatened’ and the species is known to be declining in many areas (see this blog about serious problems in Ireland). Ringing shows a particularly strong link between Finland, where breeding numbers seem to be increasing, and Britain & Ireland. The decline in British and Irish winter numbers is probably being driven by lower breeding numbers within the British Isles and in countries such as Sweden, Norway and Poland.
  • There is a theory that new generations of alpina Dunlin may be more likely to winter within Europe’s mainland estuaries, instead of continuing their westward migration across the North Sea. This might explain the apparent anomaly between the 4.1% per annum rise in Fennoscandian numbers and recent winter declines of 3% in Britain and over 20% in Ireland.

Going forwards

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Some of the survey areas were in particularly remote areas

Many of the study squares that were covered during these surveys are a long way from the main centres of human population in Norway, Sweden and Finland. The governments of the three countries are to be congratulated for supporting this important monitoring, which relied on the commitment of hundreds of volunteers. It is to be hoped that these surveys will continue and that further species-focused work will be able to explain some of the differences across Fennoscandia, particularly between eastern and western areas. The rapid declines in numbers of two species that migrate southeast each autumn (Broad-billed Sandpiper and Red-necked Phalarope) highlights the need for better information about what is happening on the flyway linking Fennoscandia with the Arabian Sea and coastal countries of the Indian Ocean.

Paper

Population trends of waders on their boreal and arctic breeding grounds in northern Europe: Åke Lindström, Martin Green, Magne Husby, John Atle Kålås, Aleksi Lehikoinen & Martin Stjernman. Wader Study 26(3)

Click on the title of paper to access it on the International Wader Study Group website. Paper is only available to members of IWSG. If you have read the whole of this blog you’ll probably want to join!

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Nesting Bar-tailed Godwit in smart summer plumage


GFA in Iceland

Graham (@grahamfappleton) has studied waders for over 40 years and is currently involved in wader research in the UK and in Iceland.  He was Director of Communications at The British Trust for Ornithology until 2013 and is now a freelance writer and broadcaster.

 

 

Red Knot pay the price for being fussy eaters!

jean-hall_36310664056_oIn a fascinating comparison of weight gained by Red Knot and Ruddy Turnstone during spring migration in Delaware Bay, on America’s east-coast flyway, Anna Tucker and colleagues show that Knot are far more vulnerable to annual variations in their main food supply than more flexible Turnstones, which target the same food if it is available. Given that changing weather patterns, associated with a warming climate, are expected to make resource availability harder to predict, the authors suggest that populations of migrant shorebirds (waders) that rely on a specific resource being available at the right time are likely to be more vulnerable – as has become apparent for Delaware Bay Knot.

Feast on the beach

Spring shorebird migration in Delaware Bay is largely fuelled by the superabundance of the eggs of horseshoe crabs. Some of the numbers associated with crabs, eggs and migratory waders are amazing!

  • Horseshoe crabs have been around for 400 million years.
  • Each spring, hundreds of thousands of horseshoe crabs swim to Delaware Bay, where the females spawn in the sand along the tidelines of Delaware and New Jersey.
  • Historically, horseshoe crabs were collected, ground up and used as fertilizer. They are still harvested for use as bait and to be bled for the pharmaceutical industry.
  • Each female crab can lay 100,000 eggs, burying them in clumps in the sand above the high tide line, over the course of a few nights.
  • Disturbance by other females and wave action brings eggs to the surface, where they become readily available to birds.
  • In a good year, egg densities on beaches can reach 800,000 per square metre, in hot-spots.
  • Over half a million shorebirds still visit Delaware Bay each spring. This number used to include 100,000 Knot but peak counts are now generally much lower, in the region of 25,000.
  • A Knot can eat 25,000 eggs a day and double its weight in two weeks.
  • Horseshoe crab eggs fuel the second stage of a Knot’s 14,000 km spring migration, from Delaware Bay to the Arctic.

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A short season

In Delaware Bay, horseshoe crabs spawn once a year, during the highest tides in May and early June, a period which overlaps with shorebird stopovers. The largest spawning events typically occur on a full-moon high tide, as long as the water temperature is higher than 15°C. Over the course of two decades, spring water temperatures have fluctuated in Delaware Bay; this annual variability in temperature is predicted to increase with climate change.

Prior to the paper by Anna Tucker and colleagues, which is at the heart of this blog, it had been shown that cooler temperatures cause delays in crab spawn, with consequences for migratory shorebirds. Anna’s research aimed to see whether Knot, which specialise on horseshoe crab eggs, are more susceptible to seasonal differences than Turnstone, which are more generalist foragers.

Knot and Turnstone both breed in the Arctic so they have similarly long journeys ahead of them when they leave Delaware Bay. The prediction was that individual Knot would show more variation in the timing and rate of mass gain than individual Turnstone and that mass gain in Knot, but not Turnstone, would be dependent on the timing of horseshoe crab spawning.

Catch, mark, weigh and re-sight

unnamed (1)Northward migration of Knot and Turnstone begins in late April/early May, with most birds arriving in Delaware Bay in mid to late May and staying for between one and two weeks, before continuing north to begin breeding in early June. The optimal breeding window in the Arctic is short and punctual arrival on territory is important if waders are to have a productive nesting season. This means that spring fattening at migration sites can directly affect breeding success. Weight data for both species were collected between 1 May and 5 June over a twenty-two-year period between 1997 and 2018, with horseshoe crab counts being made since 2003. Birds were marked with flags, with resightings in the same year providing an indication of length of stay. Recaptures of marked birds provided information on weight gain, while sightings in subsequent years gave estimates of apparent survival.

Key results from paper by Tucker et al

For both Knot and Turnstone, spring arrival was pretty consistent between years, over the 22-year period. Approximately 95% of individuals had generally arrived by the time of the seventh sampling period (26–28 May).

The proportion of horseshoe crab spawn that occurred by the time of peak shorebird arrival depended upon water temperature (see paper for details), ranging from just under a quarter (2003) to three-quarters (2004), with a median of 58%. Over the period of the study, there was no sign that the mismatch between horseshoe crab spawning and shorebird arrival was getting stronger.

unnamedMasses of most of the Knot and Turnstone caught in Delaware Bay were within the published range for the two species (Knot 125–205 g and Turnstone 84–190 g) with individually-marked Knot doubling their weight during their stay.

The estimated rate of mass gain per day varied between 2.7 g/day (2005) and 15.9 g/day (1997) for Knot and 2.2 g/day (2014) and 5.8 g/day (1998) for Turnstone. Between years, as predicted, there was far more variability in weight gain for Knot than for Turnstone, with the most pronounced difference being between the maximum rate of weight gain for individuals of the two species. The variability in this parameter for Knot was three times that for Turnstone. For both species, there were higher refuelling rates in years when mass gain started later in the season, with no trend in fattening rates, over the twenty-two-year study, for either species.

Not a lot of Knot

An earlier paper described the decline in Knot numbers in Delaware Bay and the probable link to the availability of horseshoe crab eggs. Rapid population decline in red knots: fitness consequences of decreased refuelling rates and late arrival in Delaware Bay. Allan J. Baker et al. Proceedings of the Royal Society B: Biological Sciences (2004)

  • From 1997 to 2002, an increasing proportion of knots failed to reach threshold departure masses of 180–200 g, possibly because of later arrival in the Bay and food shortage caused by over-harvesting of horseshoe crabs.
  • Resightings suggest that heavier birds in catches made between 1997 to 2002, were more likely to be seen again in subsequent years.

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This 2004 paper and subsequent annual counts of crabs and birds drew attention to overfishing problems in Delaware Bay, leading to a stakeholder-led adaptive horseshoe crab management plan, as described in this paper by McGowan et al. Developing the adaptive management plan required bringing together many groups of stakeholders, with very different values and objectives, to develop a strategy that would allow for the regulated harvest of horseshoe crabs, with a strong emphasis on protecting shorebird populations – especially Knot. The Delaware Bay horseshoe crab population now appears to be stable and it seems that shorebird populations using Delaware Bay have stabilized as well, although at much lower numbers than previously recorded in the Bay.

Conservation initiatives have restricted the impacts of the horseshoe crab fishing industry, reduced disturbance of feeding birds and showcased the importance of Delaware Bay to local people and visitors. You can learn more in this 15-minute programme: Feast on the beach http://www.delmnh.org/feast-on-the-beach/

tableAerial counts of Knot and other shorebirds have been taking place in Delaware Bay since 1981. Over this period Knot counts have varied but the big peaks of nearly 100,000 of the 1980s are now replaced by peaks that rarely exceed 25,000. See table taken from totals reported in USF&WS Rufa Red Knot background information and threats assessment. The declines in the Delaware spring passage numbers are similar in size to the drop in numbers seen wintering in Tierra del Fuego (far south of Argentina).

Why have Knot been so badly affected?

As outlined in the earlier papers and predicted at the start of the new study, the timing of pre-migratory fattening and the rate of mass gain were linked to timing of food abundance for specialist Knot but not for generalist Turnstone. Additionally, mass gain was far more variable in Knot, between years, suggesting greater sensitivity to local conditions (see figure). The way that Turnstones gain mass was more consistent across years and was not associated with abundance or availability of horseshoe crab spawn, which aligns with an ability to dig up buried eggs and switch to alternative prey items. The adaptability of Turnstone is discussed in the blog Why do Turnstone eat chips?

gain graph

The Knot is a highly adapted long-distant migrant. Studies elsewhere have shown that individual Knot can reduce the size of the gizzard, intestinal tract and organs, once they have fattened up for migration. Upon reaching Delaware Bay from southern South America, many Knot will have travelled over 6,000 miles.  The authors suggest that having an available supply of high‐quality soft‐shelled horseshoe crab eggs, which can be consumed without increasing gizzard size, may be particularly important to Delaware Bay Knot. Turnstone are thought more likely to migrate in shorter hops, a strategy that could be physiologically less challenging.

Knot refuelling was slower in years when there were more horseshoe crab eggs, suggesting that a slower mass gain is preferable and that there may be a physiological cost of rapid fat accumulation. Preliminary work (Tucker 2019) suggests that annual survival of Knot appears to be lower in years following springs in which individuals gain weight rapidly.

jean-hall_35957837470_o

In cooler years, with later horseshoe crab spawning, mass gain in Knot was faster, suggesting that birds try to “catch up” at the end of the season, to avoid a delayed departure. It would be interesting to know the upper limit of this extremely rapid mass gain, and whether there are costs to piling on the fat. Such costs could be physiological, in terms of flight efficiency, or there could be increased predation risk if vigilance is compromised while feeding more intensively, for instance.

Breeding shorebirds are constrained by a narrow time window for nesting and a fixed single‐clutch size (usually four eggs). This means that they have little flexibility to compensate for unfavourable conditions previously encountered during migration. In a warming world, with more unpredictable weather patterns, mismatches between food supply and the timing of migratory fattening could well occur more frequently, with downstream consequences for productivity and annual survival rates. The authors point out that this could be particularly bad news for populations of shorebirds that have limited capacity to vary timings within their annual cycles.

In conclusion

unnamed (3)Long‐distance migrants rely on predictable resources at stopover sites; even when these linkages are simple and predictable, populations can be vulnerable to change. The Tucker paper suggests that generalist foraging strategies, as used by Turnstone, may dampen the negative effects of phenological mismatch.

The Knot that use Delaware Bay have probably been relying upon horseshoe crab eggs for centuries and, as long as conditions remain predictable, this remains a good strategy. Over the years, there will have been cold springs, with consequent lower productivity and reduced survival, and other springs in which a superabundance of eggs has fuelled a wonderful summer of eggs, chicks and high survival. Overfishing of horseshoe crabs and more unpredictable spawning conditions appear to have tipped the balance and may (at least in part) explain huge declines in the number of Knot that visit Delaware Bay in spring. This population of Knot has been paying the price for being fussy eaters.

Details of paper

Foraging ecology mediates response to ecological mismatch during migratory stopover. Anna M Tucker, Conor P McGowan, Matthew Catalano, Audrey DeRose-Wilson, Robert A Robinson & Jordan Zimmerman. Ecosphere.

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GFA in IcelandGraham (@grahamfappleton) has studied waders for over 40 years and is currently involved in wader research in the UK and in Iceland. He was Director of Communications at The British Trust for Ornithology until 2013 and is now a freelance writer and broadcaster.

 

Migration blogs on WaderTales

wwrg GKHere’s a selection of over twenty WaderTales blogs that celebrate the wonder of shorebird migration. The focus is mainly on the East Atlantic Flyway, because that’s where I learnt about waders, but there’s a blog about the shocking drop in the numbers of waders that use the Yellow Sea migration route and an amazing story about a shorebird that links Egypt with the far east of Arctic Russia. 

Multi-species blogs

tweet long

Oystercatcher

Ringed Plover

  • RP geolocatorWell-travelled Ringed Plovers from Chukotka in north-east Russia spend the winter in Somalia, Egypt, the Red Sea & the Persian Gulf. In Chukotka these Ringed Plovers breed alongside Buff-breasted Sandpipers heading for South America, Knot that will migrate to Australia and Spoon-billed Sandpipers that may migrate to Bangladesh. It’s a small world!

Dotterel

  • Scotland’s Dotterel: still hanging on. The fate of Dotterel that breed on the plateaux in Scotland’s highest mountains may be more closely linked to changes taking place in North Africa than to warming conditions in their nesting areas.

Whimbrel

  • Whimbrels on the move summarises a paper about the movements of Icelandic, ringed Whimbrel, using ringing and colour-ringing data.
  • Iceland to Africa, non-stop discusses the speed of migration of Icelandic Whimbrel in spring and autumn.
  • Whimbrel: time to leave summarises a paper about the consistencies and variability of annual migration patterns of individual Whimbrel.
  • In search of Steppe Whimbrel summarises a migration paper about two very special individual Whimbrel. Will this knowledge help to rescue a subspecies?

blog roost flock

Bar-tailed Godwit

DSCN1827Black-tailed Godwit

The individual movements and breeding season behaviour of Icelandic Black-tailed Godwits have been studied for twenty years. They have been supported by thousands of birdwatchers who report colour-ringed birds.

Knot

  • Red Knot pay the price for being fussy eaters compares the fortunes of Knot and Turnstone that stop off in Delaware Bay. As they fatten up to travel to the Arctic, the inflexibility of Red Knot make them more prone to unpredictable food supplies (and climate change).

Sanderling

  • Travel advice for Sanderling summarises research to understand the pros & cons of spending the non-breeding season in widely different locations.

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Snipe & Jack Snipe

Common & Spotted Sandpiper

  • Not-so-Common Sandpipers mixes information about migration with a review of Common & Spotted Sandpipers by Phil Holland.

blog2 movementsGreen Sandpiper

  • Green Sandpipers and Geolocators summarises a Ringing & Migration paper about changing behaviour patterns in Green Sandpipers that wore geolocators to study their migratory journeys.

Spotted Redshank

  • Fewer Spotted Redshanks reviews migration patterns and changes in abundance of the species, in a British & Irish context.

Greenshank

  • Migration of Scottish Greenshank may seem tame when compared to the massive journeys made by birds that winter in Australia. Blog based on neat small-scale study.

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Here’s a link to the full list of WaderTales blogs. https://wadertales.wordpress.com/about/

The intention is to add one or two new blogs each month. You can sign up to receive an e-mail notification when a new one is published.

blog flock


GFA in IcelandGraham (@grahamfappleton) has studied waders for over 40 years and is currently involved in wader research in the UK and in Iceland.  He was Director of Communications at The British Trust for Ornithology until 2013 and is now a freelance writer and broadcaster.

Travel advice for Sanderling?

blog 9 wint plum ringedHave you ever seen a colour-ringed Sanderling and perhaps wondered why it spends the non-breeding* season on a British or Irish beach rather than on one in Portugal, Ghana or even further south? Why fly from Greenland to Namibia, a distance of over 20,000 km, when spending the winter months in the UK or Ireland requires a flight of as little as 3,700 km? Perhaps the chance of survival is greater in other countries or perhaps birds that travel further have a larger lifetime breeding output? A paper by Jeroen Reneerkens and colleagues provides some of the answers.

*The term non-breeding season (rather than winter season) is used in this blog because Sanderling travelling as far as Namibia experience a southern summer at the same time as UK birds are experiencing a northern winter.

Pros and cons of travelling further?

At the end of the summer, juvenile Sanderling from Greenland start heading south. The first migration might take an individual to Scotland or Namibia, in southern Africa – or anywhere in-between. The circumstances that lead to these initial settlement patterns are unknown but an individual will repeat its first migratory journey every year, with some birds travelling just 7,400 km annually and others travelling over 44,000 km. It has been argued that, for a range of migration strategies to persist, different wintering sites will have balancing pros and cons. This suggests that costs of longer migrations might be matched by benefits gained at the non-breeding destinations. Is this really true?

blog 5 juv Hebrides

Just six weeks after being ringed as a chick, this Sanderling was photographed in Mull (island off the west coast of mainland Scotland)

Using data provided by colour-ring sightings, Jeroen Reneerkens and colleagues assessed three factors that might affect the fitness of individual birds that spend the non-breeding period in different areas.

  • Annual adult survival: If a bird from one non-breeding location is more likely to survive than a bird that spends the non-breeding season somewhere else, it should live longer and potentially have more breeding attempts within a lifetime.
  • Age when a bird makes its first migration northwards: A young individual that flies north in its first spring will potentially have one more breeding opportunity than a bird that remains in the non-breeding area for its first summer.
  • Timing of migration: There is a short breeding window in the High Arctic so a bird that migrates north earlier in the spring may have higher reproductive success, because it will have a higher chance to re-nest if a first clutch is lost. (There is more about this in Time to nest again?)

Studying marked birds

map no arrowsSanderling were captured and ringed in breeding sites in northeast Greenland, at staging areas during migration (SW Iceland, N Scotland and the Dutch Wadden Sea) and in the non-breeding season (Scotland, England, Portugal, Mauritania, Ghana and Namibia). The different analyses in these studies used data from 5,863 Sanderling, of which 5,220 were individually colour-ringed.

Survival rates. By visiting key sites and collating additional reports of ringed birds from hundreds of birdwatchers, the research team were able to estimate the annual survival rates of Sanderling that spent the non-breeding season in England, France, Portugal, Mauritania, Ghana and Namibia. As can be seen in the table, the apparent survival rate in West Africa (Mauritania and Ghana) was much lower than that in Europe or Namibia. A bird with an annual survival rate of 0.75 is 67% more likely to die in any given year than a bird with a survival rate of 0.85. Confidence limits and methodological notes are provided in the paper. There is a WaderTales blog about the importance of measuring survival rates.

sa plus table

Age of first northward migration. The proportion of colour-ringed juveniles that migrated north in the first spring varied significantly, with virtually all Portuguese and English juveniles migrating north but only 35.8 % of those from Ghana and 9.6 % of those from Mauritania. (There were insufficient data to work out figures for Scotland, France and Namibia).

Timing of northward migration. Observations in Iceland provided information on the timing of migration of Sanderling from a range of non-breeding locations. This is the last possible stop-over site on northward migration, before birds migrate to their Arctic breeding sites in Greenland or Ellesmere Island in Canada. Birds from Ghana were observed in Iceland between 5 and 9 days later and those from Mauritania between 10 to 13 days later than the birds from Europe or Namibia. That is a considerable difference, given the short breeding period.

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Flock of summer plumage Sanderling, on migration in Iceland

Summary

The authors asked the question “is there equal fitness throughout the non-breeding range?”, as inferred from the three measured discussed above. The answer seems to be “no”. Sanderling from non-breeding areas in West Africa had lower annual adult survival, delayed first northward migration and later passage through Iceland than birds wintering either further north or south.

map cross Africa

Sanderling travelling north from Namibia do so by crossing the Sahara (generalised route – sample tracks are shown in paper)

Using geolocators**, the team was able to show that birds from Namibia bypassed potential staging sites in West Africa on the way north, flying north across the African continent to Europe, with some birds stopping briefly in the central part of the Mediterranean before spending a longer stop-over in NW Europe, thereby overtaking the Sanderling from West Africa. Namibian individuals used both Mauritania and Ghana as staging areas during southward migration.

** The use of geolocators is discussed in this blog.

The West African sites seem to be relatively poor places in which to spend the non-breeding months of the year. Food availability in spring is likely to be the chief problem. Theunis Piersma and colleagues have shown that the quality and biomass of prey available to shorebirds is lowest close to the equator, resulting in low fuelling rates and low body masses at departure for northward migration in Knot (Piersma et al. 2005).

Sanderling occupy a variety of different and widely-dispersed non-breeding sites between the northern tip of Scotland and the southern tip of the African continent. Here, they experience very different conditions which affect potential, life-time breeding outputs. Sites which appear to be poorer continue to be used, even though there are better options elsewhere, simply because individual birds have no knowledge of other potential areas where they could spend the non-breeding months.

A roll of the dice?

Once a juvenile Sanderling has settled upon a particular migration strategy and a spot in which to spend the non-breeding season, he or she will continue on the same annual cycle for the rest of his/her life. One of the big unknowns for waders/shorebirds – and for other groups of migrant birds for that matter – is just how these settlement patterns develop. (See Generational Change to read how young birds can create new patterns of migration).

Checking their data, Jeroen and his colleagues could see no pattern in the juvenile/adult proportions, sex ratios or sizes of the birds in different non-breeding areas that would help to explain differences in fitness. Birds from the same breeding areas of Greenland end up in non-breeding locations along the whole north-south range. It is almost as if the dice are rolled and a juvenile ends up where chance events take it.

blog 2 flying

At the level of the individual:

  • A Sanderling that spends the non-breeding season in Ghana does not know that it would have a better annual survival rate and be likely to return earlier to Greenland each spring had it ended up wintering in England or travelled as far as Namibia.
  • A bird in Namibia has no idea that it could have saved itself an accumulated migration distance of 37,000 km each year by stopping in England, without affecting its probability of survival.
  • A first-year bird that spends its first potential breeding season feeding on the beaches of Mauritania, will be unaware that first-years from Portugal have all travelled north to Greenland.

blog 8 look for crIt’s amazing what colour-ring readers have helped to discover but there is much still to learn about the migration strategies of individual waders.

Let’s hope that birdwatchers will continue to look out for colour-rings, as flocks of Sanderling chase the waves in and out on beaches throughout the world.

 

Paper in Journal of Animal Ecology

Low fitness at low latitudes: wintering in the tropics increases migratory delays and mortality rates in an arctic- breeding shorebird

Jeroen Reneerkens, Tom S. L. Versluijs, Theunis Piersma, José A. Alves, Mark Boorman, Colin Corse, Olivier Gilg, Gunnar Thor Hallgrimsson, Johannes Lang, Bob Loos, Yaa  Ntiamoa-Baidu, Alfred A. Nuoh, Peter M. Potts, Job ten Horn & Tamar Lok.

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GFA in Iceland

Graham (@grahamfappleton) has studied waders for over 40 years and is currently involved in wader research in the UK and in Iceland.  He was Director of Communications at The British Trust for Ornithology until 2013 and is now a freelance writer and broadcaster.

Sixty years of Wash waders

wwrg tt balance

Weighing a Turnstone

The Wash Wader Ringing Group (WWRG) started with a bang on 18 August 1959, when the team made a catch of 1,132 birds in a Wildfowl Trust rocket-net at Terrington, in Norfolk. Over the years, cannon have replaced rockets, catches have become generally smaller and the scientific priorities have been refined, but the Group continues to focus upon discovering more about the waders that use the Wash. This blog attempts to summarises what has been learnt about the waders that rely upon the Wash, the vast muddy estuary that lies between Lincolnshire and Norfolk, on the east coast of England.

Sixty years ago, the first goal was to understand where the vast flocks of waders that visit the Wash came from – a task that would provide great insights into the way that the whole East Atlantic Flyway works. In this time, over 300,000 birds have been caught and ringed on the Wash, as you can see in the table below. Equally importantly, hundreds of bird-ringers from across the UK and scores of visitors from around the world have joined WWRG teams, in order to learn more about the study of shorebirds. Further international collaboration has been fostered through overseas visits by WWRG members and emigration of some key personnel. The impact of the Group is truly global, as you can read in the WWRG report for 2014/2015.

wwrg table

A total of 307,226 birds is impressive, especially when some of the species totals are compared to the national totals of the BTO Ringing Scheme for the whole of Britain & Ireland since 1909. WWRG is responsible for over 40% of the Grey Plover, Knot, Sanderling and Bar-tailed Godwit, with Grey Plover topping the list at nearly 60%. These are terrific achievements for a group of volunteers. I don’t have the figures but I reckon that Nigel Clark has been responsible for the largest number of catches.

Wee quiz: What’s the best match between these Wash waders and the countries that they are quite likely to have come from? Answers at the end of the blog:

  • Species: Bar-tailed Godwit, Black-tailed Godwit, Curlew, Oystercatcher, Sanderling, Turnstone
  • Countries: Canada, Greenland, Iceland, Norway, Finland & Russia
wwrg box

Firing box connected to 4 cannon-nets

In the early days, rocket nets were borrowed from the Wildfowl Trust for an annual summer week of catches, but the development of cannon-nets gave opportunities for all-year ringing. The intensity of the Group’s activities grew in the 1970s, when there was a threat to build a freshwater reservoir on the mudflats. For a couple of years, Clive Minton (founder and leader) persuaded us to visit fortnightly, so that we could get better data on weight-gain and turn-over, using a mixture of cannon-netting and mist-netting. Everything we knew was published by the Group as The Wash Feasibility Study in 1975. These days, the Group gets together about ten times a year for catching and colour-ring-reading sessions.

wwrg oldies

By catching and ringing large numbers of the key species that visit the Wash, the Group was able to generate maps showing what are now well-known patterns of migration (see Which wader, when and why?). Early on in the Group’s history, there was a focus on nine species, with Black-tailed Godwit added as a tenth when numbers increased. Each of these species has its own section below. The maps were prepared for the Wash Wader Ringing Group 2016/2017 Report by Ryan Burrell, using data stored within the BTO archives. Blue dots represent WWRG-ringed birds that have been found abroad. Red triangles represent foreign-ringed birds caught on the Wash. The base maps used are by courtesy of Natural Earth (www.naturalearthdata.com).

Oystercatcher

wwrg map OCThe map alongside clearly demonstrates the strong link between the Wash and Norway. Other interesting things that have been discovered about Oystercatchers:

  • They live a long time. An Oystercatcher that we caught at Friskney on 30 July 1976 broke the longevity record for a BTO-ringed wader when it was shot in France on 4 April 2017 (41 years 1 month and 5 days). It was ringed as an adult so we don’t know the exact age – but it must have been at least 43 years old. There’s a WaderTales blog with a list of longevity records for BTO-ringed waders.
  • When life gets tough, Oystercatchers fail to complete their autumn moult, retaining some of their outer primaries for an extra year. The ability to complete moult and annual survival rates are both affected by cockle and mussel supplies on the Wash. There’s more about this in two papers in Biological Conservation and the Journal of Applied Ecology.

Grey Plover

wwrg GV GVIn the early days of the WWRG, Grey Plovers occurred in much smaller numbers than they do now. Writing in an article about the first 40 years of the Group, Clive Minton told the story of the first catch of 100, made in 1963, that was celebrated with three bottles of champagne provided by the late Hugh Boyd, delivering on an incentive that he had promised.

  • Over half of the Grey Plover that have been ringed in Britain & Ireland since 1909 have been ringed by WWRG since 1959 (58.9%)
  • All of the Grey Plover using the Wash breed in Siberia. Some birds spend the winter on the Wash but there are autumn moulting flocks of birds that will go on to winter in other parts of Britain & Ireland, and spring and autumn passage of birds that travel as far south as West Africa.
  • Grey Plover are late to leave the Wash, with the last departures not occurring until the start of June. Unsurprisingly, they are some of the last waders to return at the end of summer, which puts pressure on birds to finish moult before the short, cold days of winter. Some adults fail to complete primary moult, especially if food supplies are low. There is more about Grey Plover moult in this WaderTales blog.

wwrg map GV KN

Knot

wash knot

First-winter Knot (subterminal bands on wing coverts and, as yet, unmoulted juvenile fethers on upper-parts)

Knot (or Red Knot) are truly international waders, as is shown in this map of movements of islandica  (and a few canutus) birds  to and from the Wash. Several WWRG members have been heavily involved in efforts to understand the decline in numbers of the rufa subspecies in Delaware Bay (on the North American eastern seaboard) and Clive Minton has been at the heart of efforts to explain the sudden drop in survival of piersmai and rogersi adults that winter in Australia and migrate to Arctic Russia via the Yellow Sea (see Wader declines in the shrinking Yellow Sea).

  • We are still learning about Knot migration. The cluster of reports of WWRG-ringed birds in Northern Norway looks odd on this map projection but it turns out that this is a well-used stopping-off point for islandica Knot heading for northern Greenland and NE Canada. This route was first confirmed in 1985, when a joint Durham University and Tromsø University expedition caught 18 Wash-ringed birds in a total catch of 1703 birds.
  • The dot in Siberia looks odd but isn’t. This will be a bird of the canutus race, small numbers of which pause on the Wash in autumn and spring, on their way between the Russian Arctic and west Africa.
  • wwrg net set

    Setting cannon-nets

    Many birdwatchers visit the Wash in autumn and winter to see the swirling Knot flocks at Snettisham and Holme. If high tide is at first light, Knot and other waders sometimes roost on Heacham Beach, giving the occasional opportunity to make a significant catch. The most recent of these, on 11 February in 2012, included 2757 Knot, 77 of which were already wearing rings.

  • The most recent analysis of wader populations in Great Britain showed that there was a drop of nearly 20% in wintering Knot numbers (from 320k to 260k) in less than a decade (see Do population estimates matter?). Regular catches on the Wash will help produce estimates of annual survival rates and age ratios of the islandica subspecies.

Sanderling

wwrg sanderlingThe biggest catches of Sanderling are generally in the summer, when the Wash is a meeting point for birds from Greenland and Siberia. July can sometimes see catches of 200 or more birds. Traditionally, a Sanderling catch was the curtain-raiser at the start of Wash Week, an opportunity for the whole team to make one catch before splitting into ‘Terrington’ and ‘Lincolnshire’ teams for the rest of the main summer trip.

  • Wintering Sanderling on the Wash are thought to be exclusively of the race that heads northwest in the spring, to Greenland via Iceland.
  • Late summer and spring see the addition of birds passing through on their way from/to Siberian and Greenlandic breeding areas.
  • I well remember the first time we caught a Sanderling (on 26 July 1975) wearing an Italian ring (caught in Italy 9 May 1975). Thanks to Jeroen Reneerkens (whose work will be covered in an upcoming blog) I now understand that this is probably a bird that migrates from Namibia to Greenland in spring, via the Mediterranean. It will have been on its way back to Namibia when caught in July.

wwrg map SS DN

Dunlin

wash dunlin

Sam Franks, looking for the buffy tips on inner coverts, which distinguish first-year birds from adults

Nearly half of the waders caught by WWRG have been Dunlin – a total of 140,168 up until the end of 2018. There were really big flocks of Dunlin in the 1970s but numbers have dropped over the years, with peak counts now half what they were, according to WeBS data.

  • We caught over 3,500 Dunlin in one week in 1976 but the annual total has exceeded 1,000 in only four of the last ten years. Partly, this reflects a change in behaviour in the summertime, with fewer waders roosting on fields and hence less catchable.
  • Three races of Dunlin visit the UK. Our winter birds are alpina, from Siberia, NW Russia and northern Scandinavia. A lot of July birds are schinzii, breeding in the UK and as far north as Greenland, and we occasionally try to convince ourselves that we have caught an arctica from northern Greenland.
  • Data collected for the WeBS survey suggest that national winter totals have dropped by over 40% in 25 years. This could perhaps partly be explained by a redistribution of alpina, with new generations of young birds settling in wintering areas on the other side of the North Sea. Warmer winters may well make this a more practical proposition than in the 1970s. There’s more about this in this paper.

Black-tailed Godwit

wash blackwit

Newly ringed Black-tailed Godwit, caught in a mist-net at night.

Black-tailed Godwits became a priority species in 1995, when Jennifer Gill (University of East Anglia) started a project to study the movements of individuals, using colour-rings. Nearly 25 years later, the WWRG-ringed Black-tailed Godwits have contributed data to numerous papers, largely focusing upon migration.

  • The Wash is a hugely important area for moulting islandica Black-tailed Godwits. Some birds stay in East Anglia for the winter but others move south and west within the UK, west to Ireland and south to France, Portugal and Spain.
  • There are several blogs about Black-tailed Godwits in this WaderTales contents list.

Bar-tailed Godwit

One of the key things that was learned from the sudden decline in annual survival rates in a range of species that use the Yellow Sea (as mentioned above) is a need for regular monitoring of marked birds. The WWRG’s Scientific Committee set up colour-flagging projects for Bar-tailed Godwit, Curlew and Grey Plover, in order to increase the reliability of estimates of annual survival for three species that the Group does not catch in sufficient numbers to generate good retrap histories. Birdwatchers can help by reporting colour-marked birds here.

wwrg barwit map etc

  • In Bar-tailed Godwits: Migration & Survival there is a comparison of the data generated by a catch of 505 Bar-tailed Godwits in 1976 with the information that has been generated recently, using colour-flags.
  • Bar-tailed Godwits are long-lived birds. A WWRG bird holds the current record for a BTO-ringed Bar-tailed Godwit: 33 years and 11 months between ringing in 1978 and recapture in 2008. BTO longevity records are discussed in this WaderTales blog.
  • Colour-ring reading is now a significant element of Group activities, as described by Rob Pell in the WWRG Report for 2016/2017.

Curlew

Back in the 1970s, Curlew were still hunted on the Wash (paté made from autumn-shot birds was reported to be very tasty). Shooting stopped in Great Britain in 1981, when the maximum winter count on the Wash had dropped to about 3,000 birds, and by 2003/04 the maximum winter count was 15,336. Since then, numbers have declined, in line with national and international trends.

wwrg curlew map etc

  • A large number of Curlew on the Wash in winter are from Finland and surrounding countries. Surprisingly few are of UK origin.
  • Birds wearing WWRG leg-flags have been observed breeding in the Brecks (Norfolk/Suffolk).
  • The Curlew is internationally designated as ‘Near Threatened’. Is this really true when we can still see a field with 1000 roosting Curlew in Norfolk? Answers here.

Redshank

wash redshThe latest population estimates suggest that Great Britain has lost 26,000 wintering Redshank in less than a decade, representing a drop of 20%. Perhaps WWRG data can be used to help to explain these declines? Here are some of the things we know:

  • The Redshank on The Wash in the winter are mainly a mixture of birds from around the Wash, across the UK and from Iceland.
  • In cold winters, Redshank wintering on the Wash die in large numbers. After a period of severe weather in 1991, nearly 3,000 wader corpses were collected from along the tide-line, about 50% of which were Redshank. The winter WeBS counts for Redshank dropped by 50% after this mortality event but have recovered somewhat since then.
  • An analysis of nearly 1,000 dead Redshank showed that about two-thirds were of Icelandic origin. There was a tendency for smaller birds to be more susceptible to cold weather mortality than larger birds of the same species (More information in this paper by Jacquie Clark)

wwrg map RK TT

Turnstone

wash ttWinter Turnstone are birds that will head for Greenland and NE Canada in the spring but recoveries of birds in Finland and other Scandinavian countries indicate a passage of continental birds. African recoveries of WWRG-ringed birds probably include birds from Canada/Greenland and Finland/Scandinavia.

  • Turnstone wearing US Fish & Wildlife Service rings are occasionally caught on the Wash. Some of these rings were put on by Guy Morrison and his colleagues in Alert, Ellesmere Island, Canada. Guy was an early member of WWRG. It’s a small world!
  • The first Wash Turnstone were colour-ringed in 1999, as part of a study to understand why birds were feeding on the docks at Sutton Bridge. There is a WaderTales blog about the resulting paper by Jen Smart and Jennifer Gill. Colour-ringing continues, to measure annual survival rates.
  • Turnstone have a reputation for eating almost anything (including dog excrement and a human corpse) so do not be surprised if you see a colour-ringed bird scavenging for chips on the Hunstanton sea-front.

A few more highlights

Ringed Plover: this is not one of the ten key study species but 1,432 have been ringed between 1959 and 2018. Some birds are local breeders that hardly move anywhere but other birds link the Wash with Greenland, northern Norway, Morocco and Senegal.

wwrg GKGreenshank: The Group supports a colour-ringing project that was initiated by Pete Potts, in Hampshire. More information here.

Spotted Redshank: During the period 1959 to 2018, WWRG ringed a total of 85 Spotted Redshank, representing over 20% of the total ringed in Britain and Ireland since 1909. Amazingly, sixty of these birds were ringed on the same day – 27 July 1975. There is a blog about this catch and the recent decline in the number of Spotted Redshank visiting the UK. Fewer Spotted Redshanks.

Ruff: Until its closure, WWRG members spent many a smelly night at Wisbech Sewage Farm. This was a great place to catch Ruff, Curlew Sandpipers, Green Sandpipers etc. in mist-nets. Group members wrote a paper about Ruff moult and migration.

Rares: Occasionally there are surprises! WWRG has caught one each of Stone Curlew, Pectoral Sandpiper, Broad-billed Sandpiper and Terek Sandpiper. The last bird features in this WWRG blog.

What do we know now?

Migration studies have revealed the importance of the Wash to half a million or more waders each year – birds that spend the whole winter, others that refuel in the spring and vast numbers that rely on the food supplies in the mud to provide the energy for the post-breeding moult. There’s a selection of papers that have included WWRG data here, on the Group’s web-site.

wwrg cr TTThe Group still aims to maintain its general ringing programme, so that a representative sample of the key species carry rings. Colour-ringing projects aim to provide survival estimates for Curlew, Bar-tailed Godwit, Grey Plover and Turnstone, with Greenshank and Black-tailed Godwit colour-rings contributing to migration studies. Birdwatchers who visit the Wash can help by reporting colour-marked birds here, on the WWRG web-site.

WWRG data have been used to help inform decisions about the future of the Wash but the threats keep coming. Studies of migration and seasonal turn-over in numbers contributed hugely to decisions to provide national and international protection to the area and to fend off the 1970s plan to build a freshwater reservoir on the rich mudflats. The information that has been generated by many generations of volunteers over a period of sixty years has been used to manage the level of shellfish exploitation, to inform decisions about wind turbine locations and to manage activities that can cause disturbance.

The Wash Wader Ringing Group is very keen for its data to be used – and not just for impact assessment studies. Click here to learn more.

Diamond Jubilee

PLI

Phil Ireland releasing a Curlew

Over one thousand people are estimated to have contributed to sixty years of the Wash Wader Ringing Group’s activities. We have lived in barns, rolled cars, dug tens of thousands of holes, carried nets for miles, made important catches, had depressing failures, got frostbite, been threatened by surge tides and made friends for life.

In the whole of this period, there have been only two leaders of the Group – Clive Minton* (1959-1981) and Phil Ireland (1981-present). Bird ringers, wader biologists and millions of waders owe them both a huge debt of gratitude.

You can read more about the history of WWRG on the Group’s website:

*Clive Minton died in a car crash a few months after this blog was written. Friends and colleagues have shared some wonderful memories on the IWSG website.

wwrg sunset

Photo at the top of this blog is by Cathy Ryden. Many thanks to her and to other photographers.

Wee quiz:

  • Bar-tailed Godwit – Russia
  • Black-tailed Godwit – Iceland
  • Curlew – Finland
  • Oystercatcher – Norway
  • Sanderling – Greenland
  • Turnstone – Canada

 


GFA in Iceland

Graham (@grahamfappleton) has studied waders for over 40 years and is currently involved in wader research in the UK and in Iceland.  He was Director of Communications at The British Trust for Ornithology until 2013 and is now a freelance writer and broadcaster.

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Generational change

blog TGG on postIn a changing world, with more chaotic weather patterns and rapidly altering habitats, migratory birds are faced with opportunities and challenges. Long-term monitoring of colour-ringed Black-tailed Godwits, during a period of range expansion and phenological change, has revealed that individuals behave consistently over time but that the behaviour of new generations is moulded by the conditions they encounter.

A changing world 

When trying to explain observed changes in the distributions and annual cycles of migratory birds, there are many things to consider:

  • blog VM y flag

    Colour-rings enable life-time tracking. This bird, caught on its nest, had been ringed as a chick.

    Are individual birds able to take advantage of new breeding and non-breeding sites, as they become available, particularly if other areas become less suitable?

  • Are individuals able to change the timings and patterns of migration?
  • Do individuals adjust their migration routes as a consequence of changes in stop-over or wintering areas?
  • If individuals do not change what they do, how do we explain range expansions and changes in timing of migration?

Put simply, how does climate change lead to changes in distribution of migratory birds? Answering this question is key to being able to predict the rate and direction of future changes, and to assess whether our existing networks of protected sites will continue to support populations in the way that was intended. This issue was tackled by Jennifer Gill, José Alves and Tómas Gunnarsson in their paper “Mechanisms driving phenological and range change in migratory species”, published in Linking behaviour to dynamics of population and communities: applications of novel approaches in behavioural ecology and conservation, a special issue of Philosophical Transactions B (Royal Society).

Potential models

Change could happen in two main ways:

  • Individuals could relocate – having knowledge of a range of available conditions, they can choose to move elsewhere.
  • New generations could settle in new areas (in the breeding season, the non-breeding season or both) and/or adopt new migratory strategies.
blog map

Map that illustrates range expansion

Working out whether change happens through individual movement or generational shifts can only be done by life-long tracking of individuals, in populations in which range change is happening. The Icelandic population of Black-tailed Godwit is ideal for such an investigation. Black-tailed Godwits have been expanding into new breeding areas of Iceland for over 100 years, as discussed in this WaderTales blog. Population growth has been facilitated through warming spring conditions, as discussed in From local warming to range expansion.

blog TGG juvs

Naive youngsters, gathering together before migration

Icelandic Black-tailed Godwits fly south in the autumn, to spend the winter in the British Isles, The Netherlands, Belgium, France, Spain and Portugal. As numbers have grown, winter counts have increased in many areas, with new flocks appearing and expanding on estuaries and areas of wet grassland where the species was previously absent or scarce.

 

Winter distribution

The Wetland Bird Survey shows that there are three times as many Black-tailed Godwits wintering in Great Britain as there were 25 years ago. The biggest changes in numbers have occurred on estuaries in the northwest of England, with the Morecambe Bay winter maximum rising from about 180 to 3200, for instance. Where have these extra birds come from?

blog juvs on Axe

These young birds happen to have ended up on the Axe Estuary in Somerset

Black-tailed Godwits have been ringed in Iceland for nearly twenty years, providing a pool of known-age adults for which natal sites are known. Winter observations of colour-ringed individuals have shown an interesting pattern; birds breeding in newly-colonised areas, particularly in north and east Iceland, are the ones that are more likely to be found in newer winter sites.

In their paper, the authors suggest that birds nesting in these colder areas, where spring comes later, will be fledging quite late and leaving Iceland after adults have departed. With no experienced birds to follow, these young birds may well stop off at the first suitable site, many of which are in the north of the wintering range, and then they return to breed in their natal sites. Birds in Morecambe Bay don’t know that days are longer and the weather is kinder for other birds that travel further south to wintering areas such as Portugal.

blog RS Dee

Wintering birds in Northwest England

Observations from birdwatchers show that the same colour-ringed individuals are nearly always found at the same wintering sites each year. Whatever mechanism is producing this new-breeding-site to new-wintering-site link, it is becoming clear that older birds continue to do what they have always done, with changes in distribution happening as a result of a generational shift.

The annual cycle

Colour-ringed Black-tailed Godwits have been tracked for over 25 years, with a small number of individuals contributing data for the whole of this period. This tracking information can be used to ask how much individuals move around and experience different sites and to assess whether individuals from different generations are using different parts of the range.

Using colour-rings, the Black-tailed Godwit team has discovered that, although individuals can live for over 20 years, in that time they generally use a total of only about four sites between leaving Iceland in late summer and returning in the spring. Basically, individual birds have very limited experience of sites and there is no evidence that they have moved to occupy different sites as, for instance, winter conditions have changed.

blog infographic

Spring arrivals in Iceland

Colour-ring observations have shown that individual birds do not change their breeding or wintering locations and that migrating individuals often appear in the same stop-over sites year after year. The timing of movements is also pretty consistent, especially in the spring. A previous WaderTales blog called Why is spring migration getting earlier? demonstrated that the timing of  migration of individual Black-tailed Godwits varies very little, with observed shifts in the period of migration being driven by young birds returning to Iceland for the first time on average doing so somewhat earlier than previous generations. Once individual birds settle into a timing pattern, they stick to it.

blog LJ arrivals

Black-tailed Godwits, newly arrived in Iceland after crossing the Atlantic

Migration patterns

As discussed above, individual Icelandic Black-tailed Godwits have experience of only a small number of sites, which they use on an annual cycle. When migrating, a bird will generally use the same stop-over site when breaking its journey south, to undertake autumn moult, or on their way north, to take on fat for the trans-Atlantic journey. There is a range of spring migratory strategies in islandica Black-tailed Godwits, as discussed in Overtaking on migration.

blog wwrwOnce established, the annual migratory programmes of individuals rarely change, as illustrated by the map to the right. Colour-ringed Black-tailed Godwit W-WR/W regularly moulted on the Wash, in eastern England, before spending the late winter and spring in northwest England. In the late summer of 2002 he was reported at Slimbridge on 18th and 20th July but back on the Wash on the 25th. Having made the Atlantic crossing and ended up in southwest England, he was able to correct what he may have perceived to be his mistake, returning to the moulting area that he had been using since at least 1996.

Individuals might not change their annual migration routes but we do see changes in numbers on different sites that are used during migratory stop-overs. In a paper published in 2018, Mo Verhoeven and colleagues investigated whether observed changes in migratory patterns of a population of the limosa subspecies of Black-tailed Godwit were caused by individuals altering their strategies or by generational change.

Limosa Black-tailed Godwits leave breeding areas in countries such as The Netherlands in late summer, heading south to either West Africa or Iberia, where they spend the winter. In spring they all gather in staging sites in Portugal and Spain, typically on rice fields. Over the course of less than ten years, the average peak number in Extremadura (Spain) has dropped from about 24,000 to 10,000, while the numbers on the Tagus and Sado estuaries rose from 44,000 to 51,000. These changes took place during a period of rapid population decline, as described in this blog focusing on a paper by Rosemarie Kentie and colleagues.

blog VM Tagus

Limosa Black-tailed Godwits feeding in a rice field in the Tagus estuary

Mo Verhoeven et al have shown that this rapid population-level shift in spring stop-over sites from Spain to Portugal, 300 km further west, was driven by young godwits increasingly using Portugal in the period January to March, instead of Spain. Nearly all of the older birds stuck with the routes they knew. The paper is Generational shift in spring staging site use by a long-distance migratory bird.

Change happens to birds

One thing that is becoming clear in Black-tailed Godwits is that birds are being affected by change – individuals do not have the knowledge or flexibility to effect change. Even in long-lived birds, like Black-tailed Godwits, we see no evidence of individuals altering what they do over what is now two decades, despite the fact that the species’ migration dates, wintering areas and migration routes have all perceptibly changed over the same time period. It’s all about generational change. The behaviour patterns of young birds arise from the conditions they encounter in the first year of life, after which they are repeated.

Details of the Generational Change paper by Gill et al

blog LJ sum plumThe paper at the heart of this blog is: Mechanisms driving phenological and range change in migratory species by Jennifer Gill, José Alves and Tómas Gunnarsson, from the Universities of East Anglia (UK), Aveiro (Portugal) and Iceland. It is published in Linking behaviour to dynamics of population and communities: applications of novel approaches in behavioural ecology and conservation, a special issue of Philosophical Transactions B (Royal Society).

The paper could not have been produced without the help of “thousands of observers of colour-ringed godwits who have made these analyses possible”. This WaderTales blog is a celebration of the work they do: Godwits and Godwiteers.


GFA in Iceland

WaderTales blogs are written by Graham Appleton, to celebrate waders and wader research.  Many of the articles are based on previously published papers, with the aim of making wader science available to a broader audience.

@grahamfappleton

 

Time to nest again?

blog Snipe TGGEarly return to breeding areas is widely acknowledged to be ‘a good thing’ but why? Some people suggest that early migrants can choose the best territories, others argue that early chicks have a disproportionately high chance of fledging but there are other explanations too. In their paper in Ecology & Evolution, Catriona Morrison and her colleagues ask how much of the advantage of being an early migrant could be associated with having an option to nest again, if the first attempt fails.

Setting the scene

In a previous WaderTales blog, about Icelandic Black-tailed Godwits, there is clear evidence that the species is increasing in number and spreading into new breeding areas. In another blog you can read that the expansion is linked to warmer spring conditions, which allow earlier nesting. How might this change in nesting phenology influence overall productivity and contribute to the population growth in Black-tailed Godwits, and do the same processes work for other species?

blog oyc godwit

Individual Black-tailed Godwits that arrive in Iceland early each year may have a higher chance of nesting successfully, just because they have time to try again if the first nest fails

In their 2019 paper, Catriona Morrison and her colleagues from the Universities of East Anglia (UK), Iceland and Aveiro (Portugal) used a simulation model to ask whether the greater time available for laying replacement clutches can create a pattern of increased productivity among early-arriving migrants, without the need to think about territory choice or local resource availability. They suggest that early arrival can lead to greater breeding success simply because early birds have more time available to nest again, following nest loss. Within the model they explore the effect on breeding success of varying several important relationships:

  • blog Snipe nest

    This early Snipe nest might get predated but there should be time to try again

    Whether early clutches are more likely to hatch than later ones (seasonal variation in nest survival rates) – such a trend could be created by predation patterns, resource availability and opportunities to conceal nests.

  • Whether one or more replacement clutches is possible within the time available during the breeding season (number of re-nesting attempts).
  • Whether late chicks are less likely to survive and become breeding adults than earlier ones (seasonal variation in recruitment rates) – which would make re-nesting attempts less valuable.

Results

The models developed for the paper showed that, when the chance of losing a breeding attempt does not change during the course of the breeding season, species experiencing intermediate nest survival rates will benefit most from re-nesting. This makes sense; a species that has a very high chance of hatching its chicks will not need to re-nest and one that has a negligible success rate is not going to do much better if it lays more than one clutch.

blog Lapwing

This late-nesting Lapwing may not be able to defend its nest

Nest success may not be constant over the course of a season. Late pairs may find it harder to distract predators if they don’t have the support of other breeding birds, with a consequent drop in success over the summer. Alternatively, species that nests in clumps of grass, such as Snipe, might find it easier to hide their nests later in the season, thereby increasing nesting success over time.

Picking out just a few of the scenarios that are covered in more detail in the paper:

  • When nest survival rates are constant and replacement clutches are possible, early arrival increases the probability of achieving a successful nesting attempt. These benefits of early arrival can be substantial enough to persist even when late-hatched chicks (from replacement nests) are less likely to survive and recruit into adulthood.
  • If there is a seasonal decline in nest survival, late-arriving individuals will have far fewer successful nesting attempts in their lifetime than early-arrivers. In this case, laying replacement clutches only slightly increases the number of successful nesting attempts and the subsequent number of recruits.
  • If there is a seasonal increase in nest survival, early-arriving individuals will tend to lose their first clutches but these individuals have time to re-nest, and are likely to fledge the subsequent attempt. Late-arriving individuals arriving will be more likely to have a successful first attempt and hence the number of successful nesting attempts varies little with arrival date.

The main take-home message of the paper is that, in almost all of the circumstances considered, early arrival can lead to higher breeding success, simply because of the greater time available to lay replacement clutches.

Blog RP migration

What does this mean for waders?

blog Oyc nest

An Oystercatcher does not need much time to ‘build’ a nest

Repeat nesting is a common strategy in waders; a female Oystercatcher, for instance, can quite quickly lay a second clutch if the first clutch is lost. Strategies exist that can lead to a female having more than one successful brood in a season, as seen when a female Dotterel leaves a male to incubate a clutch of eggs and moves on to another male. In most circumstances, however, a pair of waders has time to raise one brood of chicks in a season, by succeeding with the first attempt or taking opportunities to lay replacement clutches if time and resources allow.

It is obvious that, if nesting success is very high, there will be little need to lay a second clutch and if success is really low, little will be achieved by laying more clutches. Waders tend to have intermediate nest-success; most are ground-nesters, making them vulnerable to a wide range of mammalian and avian predators of eggs and chicks. The scenarios modelled in the paper are particularly (but not exclusively) appropriate to breeding waders

blog Knot

Knot – a High Arctic breeder, constrained by a short season

The modelling used in this paper shows that having the time to try again is likely to increase the probability of annual success, as long as the breeding season is long enough. We know that pairs of Ringed Plovers breeding at temperate latitudes have time for several breeding attempts but pairs at high latitudes may have little chance for a second attempt, especially if nest failure occurs late in the incubation period. One way of increasing the time available to breed is to arrive earlier and the benefits of early arrival may be particularly strong for birds that occupy areas where there is a lengthening potential breeding season, something that can be made possible through climate change and warmer springs.

It is not uncommon for a breeding wader to live for five years, ten years – or even longer for larger species (WaderTales blog). During its lifetime, an individual may experience breeding seasons with differing levels of predator activity or other causes of nest loss, such as flooding or trampling, might occur. Although an individual might migrate at the same time each spring, the number of nesting attempts it will be able to fit in during any particular year will depend upon factors such as weather, prey availability and predation pressure.

blog Sanderling

Sanderling with chicks

Nest survival rates in wader populations can show seasonal declines (e.g. Sandercock 1999 – Semipalmated Sandpipers), increases (e.g. Reneerekens et al. 2016 – Sanderling) or little seasonal variation in survival (e.g. Sandercock 1999 – Western Sandpiper), but in all cases there is variability between years. All of these seasonal patterns of survival change were modelled in the Morrison et al paper. In almost every situation, a wader will have a higher chance of successfully rearing youngsters if it (and its mate) are on an early spring migration schedule.

Summary

blog Oyc

This Oystercatcher may regret nesting early! If it fails, it can try again.

Turning up early on breeding grounds in spring can potentially lead to higher reproductive success, solely as a result of the greater time available for laying a replacement clutch. Using modelling, Catriona Morrison and colleagues show that this early-arrival-benefit can be conferred even when later nesting attempts are less likely to produce successful recruits.

Advances in the timing of spring migration are occurring in many species and these findings highlight the potential role of replacement nests as a driver of population increase in those areas where repeat nesting becomes increasingly possible. Professional ornithologists and citizen scientists who study nesting birds (not just waders) are encouraged to do so for the whole season, especially by following marked individuals. Birds that wear geolocators, which can record incubation patterns for nesting attempts that would otherwise remain undetected, may be particularly helpful when trying to discover just how likely birds are to re-nest and with what success.

Only part of the story

Blog tag

Geolocator on Whimbrel

In the long run, the success of an individual bird can be measured by the number of offspring it has in its lifetime and even by the number of its genes that are present in future generations. The number of chicks that fledge each year is only part of the story, therefore. How many of these youngsters recruit to the breeding population? Do they end up breeding in areas where they will have high breeding success? Will their progeny live for a long time and hence have many opportunities to produce their own chicks? Long-term wader studies might reveal some of these answers – eventually.

Paper

blog RP chicks

The aim: a successful brood

The paper was published in Ecology & Evolution.

Why do earlier-arriving migratory birds have better breeding success? Catriona A. Morrison, José A. Alves, Tómas G. Gunnarsson, Böðvar Þórisson and Jennifer A. Gill.

DOI: https://doi.org/10.1002/ece3.5441

The paper is freely available to view.

 


GFA in Iceland

Graham (@grahamfappleton) has studied waders for over 40 years and is currently involved in wader research in the UK and in Iceland.  He was Director of Communications at The British Trust for Ornithology until 2013 and is now a freelance writer and broadcaster.